KR102111465B1 - ELECTRODE CATALYST FOR GENERATING OXYGEN CONTAINING NiFeMo OXYHYDROXIDE AND METHOD PREPARING OF THE SAME - Google Patents

Abstract

Provided is a nickel-iron-molybdenum (NiFeMo) oxyhydroxide electrocatalyst for rapid charge transfer and solid stability in an oxygen-generating reaction, and a method for preparing the electrode catalyst.

Description

Oxygen generating electrode catalyst containing NiFeMo oxyhydroxide and a method of manufacturing the electrode catalyst {ELECTRODE CATALYST FOR GENERATING OXYGEN CONTAINING NiFeMo OXYHYDROXIDE AND METHOD PREPARING OF THE SAME}

The present application provides a nickel-iron-molybdenum (NiFeMo) oxyhydroxide electrocatalyst for rapid charge transfer and robust stability in an oxygen-generating reaction, and a method for preparing the electrode catalyst.

Oxygen evolution reaction (OER) is essential to enable the production of hydrogen through water electrolysis, as well as hydrocarbon fuels with added value through carbon dioxide reduction, and thus it is necessary to develop an efficient and low-cost catalyst. However, the OER has the problem of slow charge transfer at the catalyst interfaces along with the instability of the catalyst during its repeated cycles.

Oxygen evolution reaction (OER) is a major reaction to achieve efficient energy conversion, such as hydrogen production through water splitting, and hydrocarbon fuel production through electrochemical carbon dioxide reduction. The energy required to induce the OER can be obtained from renewable energy sources, such as electrical energy from photovoltaic cells, and the use of renewable electrical energy for the OER can serve as a sustainable energy or fuel conversion technology. . However, the OER is a four-proton-coupled electron transfer reaction that limits efficiency for energy or fuel conversion. Precious metal-based oxides, including, for example, iridium oxide and ruthenium oxide, are known as efficient electrocatalysts, but the lack of the elements has delayed the commercial applications of the OER.

In principle, the activity in the OER results from the regulation of electrons in d orbitals, which induces optimized adsorption energy of oxygen intermediates ( ^* OH, ^* OOH, ^* O) adsorbed on the catalytically active site. do. Moreover, another factor that limits the OER activity is the charge transfer between the catalyst and the electrode. The OER is performed by 4-electron transfers occurring at the catalyst surface. Therefore, fast charge transfer at the reaction site affects the kinetics of the reaction. In addition, many catalysts are made of powders, and Nafion is widely used as a binder for supporting the powders on the electrode. However, the use of such a binder is undesirable for charge transfer between the catalyst and the conductive substrate, resulting in poor kinetic results.

[Advanced technical literature]

CCL McCrory, S. Jung, IM Ferrer, SM Chatman, JC Peters and TF Jaramillo, J. Am. Chem. Soc ., 2015, 137 , 4347-4357

The present application provides a nickel-iron-molybdenum (NiFeMo) oxyhydroxide electrocatalyst for rapid charge transfer and robust stability in an oxygen-generating reaction, and a method for preparing the electrode catalyst.

However, the problems to be solved by the present application are not limited to the problems mentioned above, and other problems that are not mentioned will be clearly understood by those skilled in the art from the following description.

A first aspect of the present application provides an oxygen generating electrode catalyst comprising NiFeMo oxyhydroxide.

The second aspect of the present application includes the step of subjecting a precursor solution containing a salt of Ni, a salt of Fe, and a salt of Mo to a high pressure reactor to perform a hydrothermal reaction to form NiFeMo oxyhydroxide. It provides a method for producing an electrode catalyst for oxygen generation.

According to the embodiments of the present application, a new strategy for developing a high-efficiency catalyst of a multi-metallic nickel-iron-molybdenum (NiFeMo) oxyhydroxide by combining the characteristics of enhanced charge transfer and binding energy control on the surface of the catalyst for oxygen generation is developed. to provide. As a high valence regulator, molybdenum serves to regulate the binding energy of the metal and hydroxide. In addition, microwave-assisted nitrogen plasma treatment for the catalyst leads to the formation of nanometer-scale metallic nickel domains, which promotes long-term durability as well as rapid charge transfer from the catalyst to the electrode. Consequently, the catalyst exhibits significant catalytic activity and stable cycle performance for the OER. Therefore, by the embodiments herein, a new approach for developing high performance OER catalysts is provided.

In accordance with embodiments herein, NiFeMo oxyhydride on a substrate electrode using hydrothermal synthesis using a Teflon-lined autoclave to improve contact between the catalyst and conductive substrates without using binders Rockside can be grown directly. In addition, by performing plasma treatment on the NiFeMo oxyhydroxide electrocatalyst, it is possible to further improve the charge transfer properties in the catalyst by forming metal nickel domains of a nanometer scale by locally reducing the surface of the catalyst. . For example, nitrogen plasma-treated NiFeMo oxyhydroxide exhibited a significantly low overvoltage at a Tafel slope of 43.4 mVdec- ¹ with long-term stability and stable cycle performance, surpassing the performance of conventional precious metal oxides.

1 is, in one embodiment of the present application, (a) SEM image of NiFeMo oxyhydroxide grown in nickel foam (insertion degree: low magnification image showing 3-dimensional porous nickel foam), (b) NiFeMo-N EDS mapping of ₂ , (c) HR-TEM image of NiFeMo-N ₂ showing metallic nickel domains (white circles) with size distribution (insertion), and (d) metallic nickel domains showing lattice stripes of nickel metal It shows an enlarged image of.
Figure 2, in one embodiment of the present application, shows a TEM image of NiFeMo oxyhydroxide.
3 shows, in one embodiment of the present application, PXRD patterns of NiFeMo oxyhydroxide synthesized at different temperatures.
FIG. 4 shows an attenuated total reflection FTIR (ATR-FTIR) spectrum of NiFeMo oxyhydroxide synthesized at different temperatures in one embodiment of the present application.
FIG. 5 shows HR-TEM images and size distributions of nickel metallic domains on the surface of (a) NiFeMo-H ₂ and (b) NiFeMo-H ₂ | N ₂ in one embodiment of the present application.
6 shows, in one embodiment of the present application, a FTIR spectrum of a plasma-treated NiFeMo oxyhydroxide.
FIG. 7 shows, in one embodiment of the present application, (a) Ni of plasma-treated NiFeMo oxyhydroxide and H ₂ , N ₂ , H ₂ | N ₂ plasma-treated NiFeMo oxyhydroxide. The XPS spectrum of 2p and (b) Mo 3d is shown and the XANES spectrum of (c) Ni K-edge and (d) Mo K-edge is shown.
8 shows, in one embodiment of the present application, (a) Fe of plasma-treated NiFeMo oxyhydroxide and H ₂ , N ₂ , H ₂ | N ₂ plasma-treated NiFeMo oxyhydroxide. It shows the XPS spectrum of 2p, (b) O 1s, (c) N 1s, and (d) XANES spectrum for Fe K-edge.
FIG. 9 shows, in one embodiment of the present application, (a) LSV of NiFeMo oxyhydroxide and H ₂ , N ₂ , H ₂ | N ₂ plasma-treated NiFeMo oxyhydroxide, which are plasma treated (bare). Curves, (b) Tapel plots, (c) Nyquist plot of EIS spectrum, (d) NiFeMo-N ₂ , IrO ₂ catalyst (Comparative Example) before and after the reaction (100 cycles), and NiFeMo- The results of chronopotentiometry analysis at 10 mAcm ^-2 for LSV curves (insertion degree) of N ₂ are shown.
10 shows, in one embodiment of the present application, characterization of different samples for electrocatalytic performance for time-differentiated H ₂ plasma-treated NiFeMo oxyhydroxide: (a) CV curves, (b) Tafel plots, and (c) overvoltage at 10 mAcm ⁻² , and (d) current density at 1.55 V vs RHE.
11 shows, in one embodiment of the present application, characterization of different samples for electrocatalyst performance for time-differentiated N ₂ plasma-treated NiFeMo oxyhydroxide: (a) CV curves, (b) Tafel plots, and (c) overvoltage at 10 mAcm ⁻² , and (d) current density at 1.55 V vs RHE.
12 shows, in one embodiment of the present application, characterization of different samples for electrocatalyst performance for time-differentiated H ₂ | N ₂ plasma-treated NiFeMo oxyhydroxide: (a) CV Curves, (b) Tapel plots, and (c) overvoltage at 10 mAcm ⁻² , and (d) current density at 1.55 V vs RHE.
Figure 13 is, in one embodiment of the present application, (a) NiFeMo, (b ) NiFeMo-H 2, (c) NiFeMo-N 2, and (d) NiFeMo-H ₂ | accordance with the scan rate for N ₂ A cyclic voltage current analysis is shown, and (e) a current density difference (ΔJ = J _anodic -J _cathodic ) plot for scan rates at 0.0 V vs Hg / HgO of the catalyst and (f) double layer capacitance (C _dl ) It shows.
14 shows the characterization of the IrO ₂ catalyst as a comparative example: (a) XRD patterns of the synthesized IrO ₂ powder, (b) SEM image, and (of the IrO ₂ catalyst loaded in nickel foam (NF). c) Cyclic voltage current analysis and (d) Tafel slope.
15 shows, in one embodiment of the present application, the XPS spectrum of the NiFeMo-N ₂ electrode catalyst before and after the OER cycle (a) and (b).
FIG. 16 shows, in one embodiment of the present application, (a) hydroxide of plasma-treated NiFeMo oxyhydroxide and H ₂ , N ₂ , H ₂ | N ₂ plasma-treated NiFeMo oxyhydroxide. Of the over-voltage plot of the binding energy of metals to the lockside, (b) the Tafel slope-overvoltage plot, and (c) of the oxygen evolution reaction controlled by metallic nickel domains on the plasma-treated NiFeMo oxyhydroxide surface. This is a schematic diagram.
17 shows the characterization of the NiFeO _x catalyst: (a) XRD patterns and (b) SEM image of the synthesized NiFeO _x (comparative) powder exfoliated from the nickel foam, grown in nickel foam (NF). (C) Cyclic voltage current analysis and (d) Tafel slope of the IrO ₂ (Comparative Example) catalyst.

Hereinafter, embodiments and examples of the present application will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains may easily practice. However, the present application may be implemented in various different forms and is not limited to the embodiments and examples described herein. In addition, in order to clearly describe the present invention in the drawings, parts irrelevant to the description are omitted, and like reference numerals are assigned to similar parts throughout the specification.

Throughout this specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. do.

Throughout this specification, when one member is positioned “on” another member, this includes not only the case where one member abuts another member, but also the case where another member exists between the two members.

Throughout this specification, when a part “includes” a certain component, it means that the component may further include other components, not to exclude other components, unless otherwise stated.

As used herein, the terms “about”, “substantially”, and the like are used in or near the numerical values when manufacturing and substance tolerances unique to the stated meanings are presented, to aid understanding of the present application Hazards are used to prevent unreasonable abuse by unscrupulous infringers of the disclosures that are either accurate or absolute.

The term “steps of ~” or “steps of ~” as used throughout this specification does not mean “steps for”.

Throughout the present specification, the term “combination (s)” included in the expression of the marki form means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the marki form, It means to include one or more selected from the group consisting of the above components.

Throughout this specification, the description of “A and / or B” means “A or B, or A and B”.

Hereinafter, embodiments and examples of the present application will be described in detail with reference to the accompanying drawings. However, the present application is not limited to these embodiments and examples and drawings.

The first aspect of the present application provides an electrode catalyst for oxygen generation, comprising NiFeMo oxyhydroxide.

In one embodiment of the present application, the NiFeMo oxyhydroxide may be represented by NiFeMo (O _x H _y ), but is not limited thereto. For example, in NiFeMo (O _x H _y ), x may be 1 to 2, and y may be 1 to 2, but is not limited thereto.

In one embodiment of the present application, the catalyst may be used as an electrode catalyst for generating oxygen in an electrolysis of water or an electrochemical reduction reaction system of carbon dioxide, but is not limited thereto.

In one embodiment of the present application, the catalyst may include NiFeMo oxyhydroxide grown directly on the base electrode, but is not limited thereto.

In one embodiment of the present application, the base electrode may be porous, but is not limited thereto. For example, the porous base electrode may include a metal foam or a mesh such as Ni, Cu, Ti, Al, Au, but is not limited thereto.

In one embodiment of the present application, it may be to further include a nanoparticle domain of metallic nickel formed on the surface of the NiFeMo oxyhydroxide, but is not limited thereto. In one embodiment of the present application, the size of the nanoparticles of the metallic nickel may be about 2 nm to about 8 nm, but is not limited thereto. For example, the size of the nanoparticles of metallic nickel is about 2 nm to about 8 nm, about 2 nm to about 6 nm, about 2 nm to about 4 nm, about 4 nm to about 8 nm, about 4 nm to about 6 nm, or about 6 nm to about 8 nm, but is not limited thereto.

According to embodiments herein, the plasma treatment for the NiFeMo oxyhydroxide can promote the formation of several nanometer-sized metallic nickel domains on the surface of the catalyst, which allows rapid charge transfer from the catalyst to the electrode. A route can be provided to improve the oxygen evolution (OER) activity of the catalyst.

In one embodiment of the present application, Mo contained in the NiFeMo oxyhydroxide may include oxidation states of Mo ⁶⁺ and Mo ⁴⁺ , but is not limited thereto. In one embodiment of the present application, the ratio of Mo ⁶⁺ and Mo ⁴⁺ may be about 3: about 0 to about 2, but is not limited thereto. For example, the ratio of Mo ⁶⁺ to Mo ⁴⁺ is about 3: about 0 to about 2, about 3: about 0 to about 1, about 3: about 0 to about 0.5, about 3: about 0.1 to about 2 , Or about 3: about 0.1 to about 1, but is not limited thereto.

According to embodiments of the present application, plasma treatment of the NiFeMo oxyhydroxide reduces at least a portion of Mo ⁶⁺ contained in the NiFeMo oxyhydroxide to Mo ⁴⁺ , thereby changing the coordination structure of molybdenum and The formation of a nickel metal phase according to the reduction of the elemental nickel may enable effective control of M-OH binding energies along with direct tuning of OER activity.

In one embodiment of the present application, the atomic ratio of the metal elements included in the NiFeMo oxyhydroxide may be Ni: Fe: Mo = about 2 to about 4: about 1: about 3 to about 5, but is not limited thereto. It is not. For example, the atomic ratio of the metal elements contained in the NiFeMo oxyhydroxide is about 4: about 1: about 5, about 4: about 1: about 3, about 3: about 1: about 5, or about 2: About 1: It may be about 5, but is not limited thereto.

In one embodiment of the present application, the atomic ratio of the elements included in the NiFeMo oxyhydroxide may be Ni: Fe: Mo: O = about 2 to about 4: about 1: about 3 to about 5: about 20, , But is not limited thereto. For example, the atomic ratio of the elements included in the NiFeMo oxyhydroxide is about 4: about 1: about 5: about 20, about 4: about 1: about 3: about 20, about 3: about 1: about 5 : About 20, or about 2: about 1: about 5: about 20, but is not limited thereto.

In one embodiment of the present application, when the NiFeMo oxyhydroxide is nitrogen-plasma or nitrogen / hydrogen mixed-plasma, the atomic ratio of elements to the catalyst is Ni: Fe: Mo: O: N = about 2 to About 4: about 1: about 3 to about 5: about 12 to about 20: about 0 to about 9, but is not limited thereto. In the case of nitrogen treatment, the catalyst is N-doped to contain N. For example, the atomic ratio of elements to the catalyst is about 4: about 1: about 5: about 12: about 9, about 4: about 1: about 3: about 12: about 9, about 3: about 1: about 5 : About 12: about 9, or about 2: about 1: about 5: about 12: about 9, but is not limited thereto.

In one embodiment of the present application, the NiFeMo oxyhydroxide electrocatalyst is subjected to microwave-assisted plasma treatment to further improve the charge transfer properties induced by a locally reduced surface to improve the number of nano-particles on the surface. Metric scale metallic nickel domains can be formed.

In one embodiment of the present application, the nitrogen plasma-treated NiFeMo oxyhydroxide exhibits a significantly low overvoltage at a Tafel slope of 43.4 mVdec ^-1 with long-term stability and stable cycle performance, and performance of conventional precious metal oxides Surpasses

According to embodiments herein, nitrogen plasma-treated NiFeMo oxyhydroxide is about 3 times the current density at a significantly lower overvoltage with a Tafel slope of 43.4 mVdec ^-1 with long-term stability and stable cycle performance. Can lead to improvement.

According to embodiments of the present application, the NiFeMo oxyhydroxide electrocatalyst may exhibit long-term stability over 100 hours and stable cycle performance over 100 cycles during a catalytic reaction, which may surpass the performance of a conventional noble metal iridium oxide.

According to embodiments of the present application, the plasma treatment conditions can be optimized by adjusting the plasma treatment time for the NiFeMo oxyhydroxide electrode catalyst, and the current density of NiFeMo-N ₂ is compared to a NiFeMo catalyst that is not plasma treated. Can be improved more than 3 times.

The second aspect of the present application includes injecting a precursor solution containing a salt of Ni, a salt of Fe, and a salt of Mo into a high-pressure reactor to perform hydrothermal reaction to form NiFeMo oxyhydroxide, an electrode catalyst for generating oxygen. It provides a manufacturing method.

The description of the electrode catalyst for generating oxygen according to the first aspect of the present application can be applied to all of the second aspect of the present application, and detailed descriptions of the overlapping parts are omitted, but the description is the same even if the description is omitted. Can be applied.

In one embodiment of the present application, the temperature of the hydrothermal reaction may be about 120 ° C to about 180 ° C, but is not limited thereto. For example, about 120 ° C to about 180 ° C, 120 ° C to about 170 ° C, about 120 ° C to about 160 ° C, about 120 ° C to about 150 ° C, about 120 ° C to about 140 ° C, about 130 ° C to about 180 ° C , About 130 ° C to about 170 ° C, about 130 ° C to about 160 ° C, about 130 ° C to about 150 ° C, about 130 ° C to about 140 ° C, about 140 ° C to about 180 ° C, about 140 ° C to about 170 ° C, about 140 ℃ to about 160 ℃, or may be performed in a temperature range of about 140 ℃ to about 150 ℃, but is not limited thereto.

In one embodiment of the present application, in the manufacturing method, a substrate electrode is injected with the precursor solution into the high-pressure reactor, and the NiFeMo oxyhydroxide may be directly grown on the substrate electrode by the hydrothermal reaction. However, it is not limited thereto.

In one embodiment of the present application, the salt of Ni, the salt of Fe, and the salt of Mo may each include nickel halide · hexahydrate, iron halide anhydride, molybdenum halide anhydride, but are not limited thereto. no.

In one embodiment of the present application, the salt of Ni is nickel (II) • hexahydrate, the salt of Fe is iron (III) chloride anhydride, and the salt of Mo is molybdenum chloride (V) anhydride. However, it is not limited thereto.

In one embodiment of the present application, the molar ratio of the salt of Ni, the salt of Fe, and the salt of Mo may be about 2 to about 4: about 1: about 3 to about 5, but is not limited thereto. For example, the molar ratio of the salt of Ni, the salt of Fe, and the salt of Mo is about 4: about 1: about 5, about 4: about 1: about 3, about 3: about 1: about 5, or about 2: About 1: It may be about 5, but is not limited thereto.

In one embodiment of the present application, the base electrode may be porous, but is not limited thereto. For example, the porous substrate electrode may include a metal foam or a mesh such as Ni, Cu, Ti, Al, Au, but is not limited thereto.

In one embodiment of the present application, the precursor solution may further include a linear or branched C _1-10 alkylamine as a structure modifier, but is not limited thereto. The structure modifier may be C _1-10 , C _1-8 , C _1-6 , C _1-4 , or C _1-2 , but is not limited thereto. For example, a linear or molecular type methyl amine, ethyl amine, propyl amine, butyl amine, pentyl amine, hexyl, heptyl, octyl amine may be included, but is not limited thereto.

In one embodiment of the present application, the manufacturing method may be to further include plasma treatment of the formed NiFeMo oxyhydroxide, but is not limited thereto. For example, the plasma treatment may include plasma of nitrogen, hydrogen, or a mixed gas of nitrogen and hydrogen, but is not limited thereto.

In one embodiment of the present application, by the plasma treatment, a nanoparticle domain of metallic nickel may be formed on the surface of the NiFeMo oxyhydroxide. In one embodiment of the present application, the size of the nanoparticles of the metallic nickel may be about 2 nm to about 8 nm, but is not limited thereto. For example, the size of the nanoparticles of metallic nickel is about 2 nm to about 8 nm, about 2 nm to about 6 nm, about 2 nm to about 4 nm, about 4 nm to about 8 nm, about 4 nm to about 6 nm, or about 6 nm to about 8 nm, but is not limited thereto.

Plasma treatment of the NiFeMo oxyhydroxide can promote the formation of several nanometer-sized metallic nickel domains on the surface of the catalyst, which can provide a fast charge transfer path from the catalyst to the electrode, It improves the oxygen generating reaction (OER) activity of the catalyst.

In the embodiments of the present application, at least a portion of Mo ⁶⁺ contained in the NiFeMo oxyhydroxide is reduced to Mo ⁴⁺ by the plasma treatment, thereby changing the coordination structure of molybdenum and nickel due to nickel element reduction Formation of the metal phase may enable effective tuning of M-OH binding energies with direct tuning of OER activity.

In one embodiment of the present application, the atomic ratio of the metal elements included in the NiFeMo oxyhydroxide may be Ni: Fe: Mo = about 2 to about 4: about 1: about 3 to about 5, but is not limited thereto. It is not. For example, the atomic ratio of the metal elements contained in the NiFeMo oxyhydroxide is about 4: about 1: about 5, about 4: about 1: about 3, about 3: about 1: about 5, or about 2: About 1: It may be about 5, but is not limited thereto.

In one embodiment of the present application, the atomic ratio of elements included in the NiFeMo oxyhydroxide may be Ni: Fe: Mo: O = 2 to about 4: about 1: about 3 to about 5: about 20, It is not limited thereto. For example, the atomic ratio of the elements included in the NiFeMo oxyhydroxide is about 4: about 1: about 5: about 20, about 4: about 1: about 3: about 20, about 3: about 1: about 5 : About 20, or about 2: about 1: about 5: about 20, but is not limited thereto.

In one embodiment of the present application, when the NiFeMo oxyhydroxide is nitrogen-plasma or nitrogen / hydrogen mixed-plasma, the atomic ratio of elements to the catalyst is Ni: Fe: Mo: O: N = about 2 to About 4: about 1: about 3 to about 5: about 12 to: about 20 to about 9, but is not limited thereto. For example, the atomic ratio of the elements to the catalyst is about 4: about 1: about 5: about 12: about 9, about 4: about 1: about 3: about 12: about 9, about 3: about 1: about 5 : About 12: about 9, or about 2: about 1: about 5: about 12: about 9, but is not limited thereto.

According to embodiments herein, nickel-iron-molybdenum (NiFeMo) oxyhydroxide was developed using molybdenum as a high valence control metal. NiFeMo oxyhydroxide can be directly grown in a conductive nickel foam using hydrothermal synthesis using a Teflon-lined autoclave to improve contact between the catalyst and conductive substrates without using binders. have.

Hereinafter, the present application will be described in more detail with reference to examples, but the present application is not limited thereto.

[Example]

<Substances>

Nickel (II) chloride hexahydrate (NiCl ₂ · 6H ₂ O, 99.9%), iron (III) chloride anhydride (FeCl ₃ , 99.9%), molybdenum chloride (V) anhydride (MoCl ₅ , 99.9%), chloride iridium (III) hydrate _{(IrCl 3 · H 2 O,} 98%), sodium nitrate (NaNO _3, 99%), anhydrous ethanol (99.9%), n- butyl amine _{(C 4 H 11 N, 99} %), And Nafion perfluorinated resin solution (5% by weight in a mixture of low-fat alcohol and water) were purchased from Sigma-Aldrich. Isopropyl alcohol (C ₃ H ₈ O, 99.9%) and distilled water (H ₂ O, 99.9%) were purchased from Duksan Chemicals. All chemicals were used without further purification.

<Synthesis of NiFeMo oxyhydroxide>

NiFeMo oxyhydroxide was grown by hydrothermal in a nickel foam using a Teflon-sealed stainless-steel autoclave. First, nickel foam (10 mm × 30 mm) was pretreated in dilute hydrochloric acid (HCl, 2 M) for 30 minutes to remove surface nickel oxides, and the washed nickel foam was thoroughly washed several times with water and ethanol. The precursor solution was prepared by dissolving NiCl ₂ · 6H ₂ O (0.08 mmol), FeCl ₃ (0.02 mmol) and MoCl ₅ (0.1 mmol) in ethanol (9 mL), and n-butylamine (0.5 mL) was used as the solution. Was slowly added and the solution was stirred for 30 minutes. Thereafter, the nickel foam was immersed in the solution to heat the Teflon-sealed stainless-steel autoclave to 160 ° C. for 15 hours. After cooling to room temperature, the nickel foam was washed several times with water and ethanol and dried overnight in a vacuum oven at 60 ° C. before electrochemical measurements.

<Comparative Example: NiFeO _x Synthesis of>

NiFeO _x oxide was synthesized in the same manner as the NiFeMo oxyhydroxide except that a molybdenum precursor was added to the Teflon-sealed stainless-steel autoclave. However, the total concentration of the precursor solution was adjusted to 0.2 mmol.

<Comparative example: IrO ₂ Synthesis of>

IrO ₂ was synthesized according to the following method.

30 mg of IrCl ₃ H ₂ O and 1 g of NaNO ₃ were mixed in an agate mortar to obtain a uniform powder. Then, the powder was placed in a ceramic crucible and heated in a muffle furnace at 500 ° C. for 1 hour and cooled to room temperature. Then, the powder was washed several times with water and ethanol to remove unreacted precursor, and dried in an 80 ° C. vacuum oven overnight. For electrochemical measurements, 10 mg of IrO ₂ powder was dispersed in 1 mL of water and 4 mL of isopropanol and then 20 μL of Nafion solution was added. Then, 100 μL of the solution was added dropwise to the nickel foam and dried overnight in air before measurement.

< Preparation of plasma-treated NiFeMo oxyhydroxide>

NiFeMo oxyhydroxide grown in the nickel foam was placed in a chamber of microwave plasma enhanced-chemical vapor deposition (MPE-CVD) equipment, H ₂ (99.999%, 89 sccm), N ₂ (99.999%, 91 sccm) and mixed H ₂ | N ₂ (H ₂ : N ₂ = 1: 2) generated plasma balls above the sample at microwave power of 500 W under each gas flow. Did. The pressure of the gas and the exposure time to the plasma were adjusted so that the temperature did not increase above the synthesis temperature of 160 ° C. After exposure to the plasma ball, the color of the sample changed from brown to dark brown.

< Characteristic analysis>

Scanning electron microscopy (SEM) images were obtained with a field emission scanning electron microscope (JEM-7600F, JEOL, Japan) operated at 15 kV. Transmission electron microscopy (TEM) images were obtained using a transmission electron microscope (Tecnai F20, FEI Company, USA) at an accelerated voltage of 200 kV. Powder X-ray diffraction (PXRD) patterns were obtained on an X-ray diffraction analyzer (Smartlab, Rigaku, Japan) using a 1200 W (40 kV, 30 mA) Cu-Kα radiation source. X-ray photoelectron spectroscopy (XPS) spectra are X-ray photoelectron spectroscopy (K-alpha, Thermo Scientific, using Al-Kα radiation at a beam current of 3 mA and a beam size of 0.4 mm. USA). Infrared spectra were obtained with a Fourier transform infrared spectroscopy (FT / IR-6100FV, JASCO, USA) using an attenuated total reflectance (ATR) technique with a ZnSe window. X-ray adsorption spectroscopy (XAS) was performed at the Pohang Accelerator Laboratory (PAL, Korea), and the operating energy was 3.0 GeV at a maximum storage current of 300 mA. XANES measurements were performed on a 7D beam line. The radiations of the bending magnet and tapered vacuum undulator were monochromatized using a Si (111) double crystal monochromator. The incident beam was detuned to the proper ratio for harmonic removal.

<Electrochemical measurement>

All electrochemical measurements were made with a potentiometer (SP-240, Biologic Science Instruments, USA) using a three-electrode system with Hg / HgO (filled with 1 M KOH) and Pt wires as reference and counter electrodes, respectively. It was carried out at room temperature. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were performed at 5 mVs ^-1 with 95% iR correction. Oxygen evolution reaction was performed in 1 M KOH and the solution was purged with O ₂ (99.999%) for 30 min before each experiment. The positive potential electrochemical impedance spectrum (PEIS) was obtained in the frequency range of 1 MHz to 100 mHz.

Morphological analysis

NiFeMo oxyhydroxide was grown in a highly porous nickel foam through hydrothermal synthesis, and the morphology of the catalyst grown in the nickel foam was observed with a scanning electron microscope (SEM). 1A shows that NiFeMo oxyhydroxide catalysts are densely grown in a porous nickel foam, and transmission electron microscopy (TEM) images (FIG. 2) show that the catalyst has a curved sheet-like structure. In addition, powder X-ray diffraction (PXRD) patterns (FIG. 3) and Fourier transform infrared spectroscopy (FTIR) spectra (FIG. 4) show multimetallic NiFeMo oxyhydroxide. It was synthesized at an optimized temperature of 160 ° C. According to the energy dispersive spectroscopy (EDS-TEM) of NiFeMo oxyhydroxide, the ratio of the components (Ni, Fe, Mo) was adjusted to 4: 1: 5 (Table 1). Table 1 shows the energy dispersion spectrum results of NiFeMo oxyhydroxide.

[Table 1]

Thereafter, plasma treatment was performed using microwave plasma-enhanced chemical vapor deposition (MPE-CVD) by adjusting the plasma exposure time and plasma type for the NiFeMo oxyhydroxide catalyst. We prepared three types of catalysts using different plasma treatments: hydrogen plasma (NiFeMo-H ₂ ), nitrogen plasma (NiFeMo-N ₂ ), and a mixed plasma of hydrogen and nitrogen (NiFeMo-H ₂ | N ₂ ). The catalyst grown in the nickel foam was placed in a chamber, and bright plasma balls were formed on the sample for several minutes under H ₂ and N ₂ atmosphere. The colors of the plasma were changed according to the type of gas (pink for hydrogen and orange for oxygen). After the plasma treatment, the morphology of NiFeMo oxyhydroxide was observed with high-resolution TEM (HR-TEM). In FIG. 1B, the EDS mapping images confirmed that the iron and molybdenum atoms were uniformly distributed in the oxyhydroxide. However, after the plasma treatment, nickel atoms aggregated and formed aggregation domains. In FIG. 1C, the HR-TEM image on the surface of the catalyst of NiFeMo-N ₂ showed that nanometer-sized particle domains with an average diameter of 2.8 nm were observed. Moreover, larger domains with mean diameters of 4.5 nm and 3.9 nm, respectively, were observed in NiFeMo-H ₂ and NiFeMo-H ₂ | N ₂ (FIG. 5). The plane distances of the domains were measured to be 0.204 nm and 0.178 nm using selected area electron diffraction (SAED) patterns, which correspond to lattice surfaces 111 and 200 of crystalline nickel metal, respectively. It was revealed (Fig. 1d). These results support the formation of the metallic nickel domains on the surface of the plasma-treated NiFeMo catalyst. Moreover, it can be seen that uniform and smaller sized metallic nickel domains were generated under nitrogen plasma. However, the FTIR spectrum shows that the surface (oxy) hydroxide functional groups remain slightly reduced with M-OH stretching peaks after plasma (Figure 6).

Structural analysis

The chemical states of the elements were determined using X-ray photoelectron spectroscopy (XPS). According to the XPS fitting results of the Ni 2p spectrum shown in FIG. 7A, NiFeMo oxyhydroxides had peaks of 857.5 eV and 875.1 eV corresponding to Ni ³⁺ 2p _3/2 and Ni ³⁺ 2p _1/2 , respectively. , Both Ni ²⁺ and Ni ³⁺ states at peaks of 855.5 eV and 872.9 eV corresponding to Ni ²⁺ 2p _3/2 and Ni ²⁺ 2p _1/2 . However, the XPS spectrum showed that at a peak of 853.0 eV, the metallic Ni ⁰ state was generated after plasma treatment regardless of the type of plasma. These results are consistent with the formation of nickel metal domains on the surface that we observed in the TEM images and their SAED patterns. The XPS spectrum of Mo 3d is shown in FIG. 7B, where the two peaks of 232.1 eV and 235.2 eV correspond to Mo ⁶⁺ 3d _5/2 and Mo ⁶⁺ 3d _3/2 , respectively. However, plasma treatment induced partial reduction from Mo ⁶⁺ to Mo ⁴⁺ , which induced two peaks at 230.3 eV (Mo ⁴⁺ 3d _5/2 ) and 233.5 eV (Mo ⁴⁺ 3d _3/2 ). . The XPS spectra of different species (Fe, O, N) were also determined as shown in FIG. 8.

In the Fe 2p spectrum of FIG. 8, no significant change was observed in the valence state of Fe ³⁺ (725 eV, 711 eV), but satellite peaks were increased for NiFeMo-H ₂ and NiFeMo-H ₂ | N ₂ . O 1s spectra are oxygen adsorbed water (M- ^* H ₂ O, 533.2 eV), hydroxide or oxyhydroxide (M-OH and M-OOH, 531.7 eV) and lattice oxygen. (MO, 530.2 eV). After plasma treatment, it was found that the proportion of lattice oxygen increased. The N 1s spectrum showed that nitrogen (400.0 eV) was present in NiFeMo-N ₂ and NiFeMo-H ₂ | N ₂ . In addition, Mo ⁶⁺ (398.0 eV) peak appeared due to Mo 3p overlap, whereas Mo ⁴⁺ (395.7 eV) peak was observed due to reduction of Mo species after plasma treatment. This demonstrates that Mo atoms were reduced from Mo ⁶⁺ to Mo ⁴⁺ after plasma treatment.

X-ray absorption near-edge spectroscopy (XANES) results of nickel and molybdenum account for changes in atomic structure of plasma-treated NiFeMo oxyhydroxide. In FIG. 7C, an increase in intensity of the white line peak was observed by plasma treatment, suggesting that the coordination environment of nickel was well aligned, and the result was consistent with the increase of lattice oxygen peaks observed in the XPS spectrum of O 1s. (Fig. 8B). However, no significant shift in the nickel K-edge position was observed, which means that the oxidation state of most nickel did not change after plasma treatment. The Mo K-edge XANES spectrum of NiFeMo oxyhydroxide is shown in Figure 7d. As also estimated from the XPS spectrum of 7b, after the position of the K- edge plasma treatment (H ₂ and N ₂₎ left-mutations were, which, as in Figure 7b the estimated from the XPS spectrum, in the Mo ⁶⁺ Reduction of oxidation state to Mo ⁴⁺ . In addition, the pre-edge peak Mo K-edge of the NiFeMo-H ₂ increased and the left side shifted, but no change was observed for NiFeMo-N ₂ and NiFeMo-H ₂ | N ₂ . The above results indicate that the coordination environment of molybdenum in NiFeMo-H ₂ was changed.

Electrochemical performance

To evaluate the electrocatalytic OER performance of NiFeMo oxyhydroxide, a linear sweep voltammetry (LSV) was performed using a 3-electrode structure in O ₂ -saturated aqueous 1 M KOH electrolyte. All polarization curves were iR -corrected to compensate for external resistance and measured at scan rates of 5 mVs ^{-1 for} LSV curves and 1 mVs ^-1 for Tafel plots. As shown in FIG. 9A, NiFeMo, NiFeMo-H ₂ , NiFeMo-N ₂ , and NiFeMo-H ₂ | N ₂ catalysts were 249 mV, 231 mV, 226 mV, and 240 mV, respectively, at a current density of 10 mAcm ⁻² , respectively. Significantly low overvoltage. 10 to 12, the plasma treatment conditions were optimized by adjusting the plasma treatment time, and the optimum treatment time was found to be about 5 minutes. The current densities of NiFeMo, NiFeMo-H ₂ , NiFeMo-N ₂ , and NiFeMo-H ₂ | N ₂ at 300 mV overvoltage were 95 mAcm ^-2 , 255 mAcm ^-2 , 330 mAcm ^-2 and 154 mAcm ^{-2 respectively} . . It is noted that the current density of NiFeMo-N ₂ has been improved more than three times as compared to the NiFeMo catalyst without plasma treatment. In addition, as shown in FIG. 9B, tapel slopes were obtained from the tapel plot. The tapel slope of NiFeMo-N ₂ was 43.4 mVdec ^-1 , which was the tapel of NiFeMo (50.8 mVdec ^-1 ), NiFeMo-H ₂ (44.7 mVdec ^-1 ), and NiFeMo-H ₂ | N ₂ (49.1 mVdec ^-1 ). Smaller than the slopes. The results indicate that the surface metallic nickel domains formed in the NiFeMo catalyst enhance OER kinetics, thereby increasing the OER reaction rates at the catalytically active site. In addition, electrochemically active surface area (ECSA) in FIG. 13 was evaluated using the bi-layer capacitance (C _dl ) of the catalyst. The slope of the current density for scan speeds is equal to twice the C _dl , and the slope is 23.5 mFcm ^-2 (NiFeMo), 18.4 mFcm ^-2 (NiFeMo-H ₂ ), 18.4 mFcm ^-2 (NiFeMo-N ₂ ), And 13.9 mFcm ^-2 (NiFeMo-H ₂ | N ₂ ). This means that the number of active sites was reduced by plasma treatment, and the OER dynamics was not related to the number of active sites.

In addition, potentiostatic electrochemical impedance spectroscopy (PEIS) measurements were performed at 1.5 V vs reversible hydrogen electrode (RHE) during the OER to analyze charge transfer characteristics. In FIG. 9C, Nyquist plots of the PEIS spectrum showed that all the catalysts had similar series resistance (R _s ) values of less than 1 Ω. However, the charge transfer resistance (R _ct ) values at the interface between the catalyst and the electrolyte, which are the radius of the semicircle of NiFeMo, NiFeMo-H ₂ , NiFeMo-N ₂ and NiFeMo-H ₂ | N ₂ , are 2.13 Ω, respectively. , 0.58 Ω, 0.52 Ω and 0.77 Ω. According to the above results, the inventors found that the conductivity of the samples was significantly improved by the formation of conductive metallic nickel domains on the surface of the NiFeMo catalyst by plasma treatment. In addition, the smaller sized metallic nickel domains of NiFeMo-N ₂ promoted faster charge transfer between the catalytically active sites of the catalyst and oxygen intermediates in the electrolyte. The long-term stability of the highest performance NiFeMo-N ₂ catalyst was also demonstrated by evaluating the durability of the catalyst by chronopotentiometry at 10 mAcm ⁻² for 100 hours at operating conditions (FIG. 9D). Unlike the IrO ₂ catalyst loaded on the nickel foam (FIG. 14), the catalyst did not exfoliate or oxidize metallic nickel domains and the overvoltage of the catalyst of this example remained almost unchanged (FIG. 15). In addition, the NiFeMo-N ₂ catalyst showed negligible changes in LSV curves even after 100 cycles.

In Fig. 15, in order to obtain a spectrum of the nickel element, a powder of NiFeMo oxyhydroxide was attached to carbon paper using a Nafion solution.

In FIG. 16A, overvoltage plots for the binding energy of metal and hydroxide (M-OH) were obtained for NiFeMo oxyhydroxide, NiFeO _x (FIG. 17), and IrO ₂ , so that the OER activity and binding energies The relationship between them was established. The present inventors have prepared catalysts by linear interpolation of enthalpy change produced in oxidation of materials containing Ni (OH) ₃ , Fe (OH) ₃ , Mo (OH) ₆ and Ir (OH) ₃ The M-OH binding energies for were measured. Nickel and iron have a strong binding energy with hydroxide, but the binding energy of the high valence molybdenum metal is relatively weak. This indicates that the addition of molybdenum enables effective control of M-OH binding energies with direct tuning of the OER activity of the catalyst. The catalytic activity can be tuned by the addition of control metals (FIG. 16B), but through surface plasma treatment the kinetics provide a metallic nickel domain that provides a fast charge transfer path from the active site to the electrode as shown in FIG. 16C. The dynamics are enhanced from their formation.

In summary, the present inventors use molybdenum as a high valence control metal to provide a multi-metallic electrocatalyst for the OER, namely nickel-iron-molybdenum (NiFeMo) oxyhydroxide. In addition, microwave-assisted plasma treatment of NiFeMo electrocatalysts has been found to promote the formation of several nanometer-sized metallic nickel domains on the surface, which provides a fast charge transfer path from the catalyst to the electrode. The nitrogen-plasma-treated NiFeMo-N ₂ catalyst has a long-term stability of 100 hours or more and a stable cycle performance of 100 cycles or more, and requires a low overvoltage of 226 mV to reach a current density of 10 mAcm ^-2 . As a result, the present inventors provide a new route for the design of an excellent electrocatalyst with high activity and durability in OER through introduction of the control metals herein and easy plasma-induced surface modification.

The foregoing description of the present application is for illustration, and a person having ordinary knowledge in the technical field to which the present application belongs will understand that it is possible to easily change to other specific forms without changing the technical spirit or essential characteristics of the present application. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present application is indicated by the claims to be described later rather than the above detailed description, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts should be interpreted to be included in the scope of the present application. .

Claims (17)

An electrode catalyst for oxygen generation, comprising a nanoparticle domain of 2 nm to 8 nm of metallic nickel formed on the surface of NiFeMo oxyhydroxide and the NiFeMo oxyhydroxide.
According to claim 1,
The NiFeMo oxyhydroxide is grown directly on the base electrode, an oxygen generating electrode catalyst.
According to claim 2,
The substrate electrode is porous, the electrode catalyst for oxygen generation.
According to claim 2,
The base electrode is an electrode catalyst for generating oxygen, which includes a metal foam or a mesh.
delete According to claim 1,
The atomic ratio of the elements included in the NiFeMo oxyhydroxide is Ni: Fe: Mo: O = 2 to 4: 1: 3 to 5:20, an electrode catalyst for oxygen generation.
According to claim 1,
Mo contained in the NiFeMo oxyhydroxide is to include the oxidation state of Mo ⁶⁺ and Mo ^4+, the electrode catalyst for oxygen generation.
According to claim 1,
An electrode catalyst for oxygen generation, which is used as an electrode catalyst for oxygen generation in an electrolysis of water or an electrochemical reduction reaction of carbon dioxide.
Injecting a precursor solution containing a salt of Ni, a salt of Fe, and a salt of Mo into a high pressure reactor to perform a hydrothermal reaction to form NiFeMo oxyhydroxide, and
Plasma treatment of the formed NiFeMo oxyhydroxide
A method for producing an electrode catalyst for oxygen generation according to any one of claims 1 to 4 and 6 to 8.
The method of claim 9,
A method of manufacturing an electrode catalyst for oxygen generation, wherein a substrate electrode is injected into the high-pressure reactor together with the precursor solution, and the NiFeMo oxyhydroxide is directly grown on the substrate electrode by the hydrothermal reaction.
The method of claim 9,
The precursor solution is to further include a linear or branched C _1-10 alkylamine as a structure regulator, a method for producing an electrode catalyst for oxygen generation.
The method of claim 10,
The substrate electrode is porous, a method for producing an electrode catalyst for generating oxygen.
The method of claim 12,
The base electrode comprises a metal foam (foam) or mesh, a method for producing an electrode catalyst for oxygen generation.
delete The method of claim 9,
The plasma treatment includes nitrogen, hydrogen, or a plasma of nitrogen and a mixed gas of hydrogen, a method for producing an electrode catalyst for oxygen generation.

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